Urban Tree Growth Characteristics of Four Common Species in South Germany

Urban trees are important, green features of cities. However, knowledge of the size development of frequently planted tree species, which is the basis for modeling environmental benefits of urban trees, is mostly limited. Within this study, allometric relationships for tree structures like tree height, crown parameters, and leaf area were developed for 4 common urban tree species in South Germany (horse chestnut [Aesculus hippocastanum], small-leaved lime [Tilia cordata], black locust [Robinia pseudoacacia], and plane tree [Platanus × hispanica]). Growth and size differences between different tree species, cities, and planting sites (street, park, square) were analyzed. Moreover, the above- and belowground growing conditions were compared and their influences on growth analyzed. Marked differences in the structural development between species were found, mostly due to their species characteristics. Fast growing species (e.g., R. pseudoacacia) also showed fastest development of the tree structures compared to other species. Differences between cities were minor, especially for trees younger than 100 years, whereas the variation of growing conditions within cities strongly influenced their growth. Park trees mostly had greater tree structures compared to trees at other growing sites, though this was also species-dependent. Above- and belowground conditions varied between species, cities, and sites (street, park, square), with obstacles (trees, buildings) south of the trees having a negative influence on crown growth. These patterns can be helpful for better planning of green features in cities. They provide a basis for urban tree management based on the growing space requirements of tree species and their ecosystem service provision.